Propeller shaft and yoke structure of universal joint used for the propeller shaft

ABSTRACT

A propeller shaft includes a shaft part and a a first yoke having a fixing portion, a connecting portion, a first yoke portion and a first concave portion. The connecting portion is provided apart from a first concave portion in the direction of the rotation axis of the shaft part. An outside diameter of the connecting portion is greater than an outside diameter of the shaft part in a radial direction of the rotation axis of the shaft part.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/789,808, filed on Oct. 20, 2017, which is a continuation of U.S.application Ser. No. 15/414,071, filed Jan. 24, 2017, now U.S. Pat. No.9,850,959 issued Dec. 26, 2017, which is a continuation of U.S.application Ser. No. 15/094,095, filed Apr. 8, 2016, now U.S. Pat. No.9,605,716 issued on Mar. 28, 2017, which is continuation of U.S.application Ser. No. 14/287,350, filed May 27, 2014, now U.S. Pat. No.9,334,904, issued on May 10, 2016, which claims priority from JapanesePatent Application No. 2013-112667, filed on May 29, 2013, thedisclosures of which are expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a propeller shaft, for instance, for avehicle, and also relates to a yoke structure of a universal joint usedfor the propeller shaft.

As a related art propeller shaft, Japanese Patent ProvisionalPublication No. 2008-208919 (hereinafter is referred to as“JP2008-208919”) discloses the propeller shaft.

As is known in the art, this propeller shaft is a propeller shaft thattransmits a driving force of an engine, which is outputted from atransmission mounted on a front side of a vehicle, to a differentialgear mounted on a rear side of the vehicle. The propeller shaft and thetransmission are coupled together by the fact that a yoke of a universaljoint provided at a front end portion of the propeller shaft and aconnecting member provided at a top end portion of an output shaft ofthe transmission are connected by tightening of bolt and nut.

The yoke has a substantially rectangular mounting flange in which fourbolt insertion holes are formed at four corners and has a pair of yokeportions having a bifurcated shape which protrude from one side surfaceof the mounting flange. On the other hand, the connecting member has asubstantially circular flange portion that is made abut on or touchesthe mounting flange from an axial direction. Four bolts, e.g. four studbolts, which are inserted into the four bolt insertion holes are fixedto this flange portion at four points in a circumferential direction ofthe flange portion. The yoke of the propeller shaft and the connectingmember of the output shaft of the transmission are connected, throughthe mounting flange of the yoke and the flange portion of the connectingmember, by screwing the nut onto the stud bolt and tightening it using aturning tool (a tightening tool), e.g. a socket wrench.

SUMMARY OF THE INVENTION

In recent years, weight reduction and commonality of components havebeen achieved, also sizes of the transmission and the differential gear,which each of both ends of the propeller shaft is connected to, havebeen reduced. In response to this trend, each bolt circle diameter ofthe mounting flange at the propeller shaft side and the flange portionof the connecting member at the transmission side, namely a circlediameter of the stud bolt and a circle diameter of the bolt insertionhole, become smaller.

Because of this size reduction of the bolt circle diameter, a fixingposition of each stud bolt and a forming position of each bolt insertionhole are shifted to an axial center of the yoke, and a gap or clearancebetween the nut and a side surface of the yoke portion is limited orrestrained. Then, when inserting the socket wrench onto the nut, thesocket wrench interferes with the side surface of the yoke portion, thusthis causes difficulty in inserting or fitting the socket wrench to thegap.

Further, even if the socket wrench can be inserted or fitted to the gap,since the socket wrench requires pulling out linearly along a longlength of an axial direction of the bolt when detaching the socketwrench, the detaching work is also difficult. These difficulties ininserting and detaching the socket wrench result in efficiency andworkability of a connecting work (fastening or tightening work) of thepropeller shaft decreasing.

It is therefore an object of the present invention to provide apropeller shaft and a yoke structure of a universal joint used for thepropeller shaft which are capable of increasing efficiency andworkability of a connecting work of the propeller shaft.

According to one aspect of the present invention, a propeller shaftcomprises: a first yoke having; (a) a fixing portion fixed to a shaftpart; (b) a pair of first yoke portion shaving a bifurcated shape thatextends from one end portion of the fixing portion in an axialdirection; and (c) a first bearing hole formed at a top end portion ofeach first yoke portion and securing therein a first bearing that holdsa cruciform shaft; a second yoke coupled to the first yoke through thecruciform shaft and secured to a predetermined member, the second yokehaving; (d) a mounting flange; and (e) a bolt insertion hole formed atthe mounting flange, a bolt to secure the second yoke to thepredetermined member being inserted into the bolt insertion hole; and asecuring member securing the mounting flange of the second yoke to thepredetermined member through the bolt by a fastening tool, and a firstconcave portion to slide thereon an outer circumferential surface of thefastening tools provided at each first yoke portion.

According to another aspect of the present invention, a propeller shaftcomprises: a ball yoke having; (a) a cylinder portion whose one end isfixed to a shaft part; (b) a pair of first yoke portions having abifurcated shape that extends from one end portion of the cylinderportioning an axial direction, each first yoke portion being provided ata top end portion thereof with a bearing hole securing a bearing thatholds a cruciform shaft; a flange yoke coupled to the ball yoke throughthe cruciform shaft and secured to a predetermined member, the flangeyoke having; (c) a flange; and (d) a bolt insertion hole formed at theflange, a bolt to secure the flange yoke to the predetermined memberbeing inserted into the bolt insertion hole; and a unscrewed onto thebolt from a flange yoke side by a fastening tool, and a first concaveportion to slide thereon an outer circumferential surface of thefastening tool is provided at a side surface of each first yoke portionalong an axial direction of the bolt inserted into the bolt insertionhole.

According to a further aspect of the invention, a yoke structure of auniversal joint comprises: a fixing portion fixed to a shaft part of apropeller shaft; a pair of bifurcated yoke portions extending from thefixing portion in an axial direction; and a bearing hole formed at eachyoke portion and securing therein a bearing that holds a cruciformshaft, and the yoke portion is provided with a concave portion thatsuppresses an interference of an outer circumferential surface of afastening tool that fastens a nut and a bolt for securing the propellershaft to a connecting member on a vehicle side with a side surface ofthe yoke portion.

According to the present invention, especially when detaching or pullingout the fastening tool from the securing member after fastening thesecuring member, the interference of the outer circumferential surfaceof the fastening tool with the side surface of the first yoke portioncan be suppressed.

The other objects and features of this invention will become understoodfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is general view of a propeller shaft of the present invention.

FIG. 2 is a perspective view of a first universal joint according to afirst embodiment of the present invention.

FIG. 3 is a front view of a yoke according to the first embodiment.

FIG. 4 is a perspective view for explaining a connecting work of thepropeller shaft according to the first embodiment.

FIG. 5 is a perspective view for explaining the connecting work of thepropeller shaft according to the first embodiment.

FIG. 6 is a side view for explaining the connecting work of thepropeller shaft according to the first embodiment.

FIG. 7 is a side view for explaining the connecting work of thepropeller shaft according to the first embodiment.

FIG. 8 is an enlarged view of a main part of A in FIG. 7 for explainingthe connecting work of the propeller shaft according to the firstembodiment.

FIG. 9 is a front view of a second yoke according to a second embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of a propeller shaft and a yoke structure of a universaljoint used for the propeller shaft of the present invention will beexplained below with reference to the drawings. In the embodiments, thepropeller shaft is applied to a vehicle.

First Embodiment

As shown in FIG. 1, a propeller shaft 1 has a structure in which a firstshaft part 2 on a vehicle front side and a second shaft part 3 on avehicle rear side are coupled together through a constant velocityuniversal joint 4 provided at a front end portion of the second shaftpart 3.

This propeller shaft 1 is coupled to an output shaft of a transmission(not shown) through a first universal joint 5 provided at a front endportion of the first shaft part 2. On the other hand, the propellershaft 1 is coupled to an input shaft of a differential gear (not shown)through a second universal joint 6 provided at a rear end portion of thesecond shaft part 3, and is set so as to be able to wobble or rock inup-and-down directions and right-and-left directions of the vehicle.

The propeller shaft 1 is rotatably supported by a center bearing 7provided between the first shaft part 2 and the constant velocityuniversal joint 4. Further, the propeller shaft 1 is supported and fixedto a floor bottom of the vehicle through a supporting member 8 that issecured to the center bearing 7. General bending or flexure of thepropeller shaft 1 is suppressed by such a supporting and fixingstructure.

The first universal joint 5 and the second universal joint 6 are aso-called cruciform universal joint. Although shapes of these first andsecond universal joints 5 and 6 connecting to the transmission at afront side of the propeller shaft 1 and the differential gear at a rearside of the propeller shaft 1 respectively are slightly different fromeach other, their basic structures are the same. Thus, in the followingdescription, only the first universal joint 5 will be explained indetail.

As shown in FIG. 2, the first universal joint 5 mainly has a ball yoke 9that is a first yoke fixed to the front end portion of the first shaftpart 2, a flange yoke 10 that is a second yoke coupled to the outputshaft of the transmission through a connecting member 11 (describedlater) and a cruciform shaft 12 that is installed between the yokes 9and 10 and rockably supports these yokes 9 and 10 in the in up-and-downand right-and-left directions.

As can be seen in FIG. 2, the ball yoke 9 is formed by a cylinderportion 9 a having a substantially same diameter as a front edge of thefirst shaft part 2 and a pair of first yoke portions 9 b, 9 b formedintegrally with a top end of the cylinder portion 9 a and having abifurcated shape which protrude or extend along an axial direction.These cylinder portion 9 a and first yoke portions 9 b, 9 b are formedas a single-piece component by casting.

The cylinder portion 9 a is joined to the first shaft part 2 from theaxial direction through friction welding of a rear end portion 9 c andthe front end portion of the first shaft part 2.

Each of the first yoke portions 9 b, 9 b is provided at both sidesurfaces thereof with a first depressed portion 13 that is a firsthollow portion (or a first concave portion). This first depressedportion 13 is formed into an arc-shaped groove in cross section which issubstantially same as an arc shape of an outer circumferential surface19 d (described later) of a socket wrench 19. Further, the firstdepressed portion 13 extends from a front end portion side of each firstyoke portion 9 b up to an almost middle position in the axial directionon an outer circumferential surface of the cylinder portion 9 a. Morespecifically, as seen in FIG. 2, the first depressed portion 13 isformed so as to gradually spread (so as to gradually become wider) froma top end portion 13 a at the front end side of the first yoke portion 9b up to a rear end portion 13 b at the cylinder portion 9 a side. Adepth of the groove is formed so as to gradually become deeper from thetop end portion 13 a side according to a reverse taper angle of bothside surfaces of the first yoke portion 9 b, and a middle position in awidth direction of the groove is deepest.

Further, as shown also in FIG. 8, a rear edge of the rear end portion 13b at the cylinder portion 9 a side, of the first depressed portion 13 isshaped into an inclined surface 13 c having a reverse tapered shapewhich rises toward the outer circumferential surface of the cylinderportion 9 a.

The inclined surface 13 c (A circumferential direction of the inclinedsurface 13 c) is formed so as to face toward the first yoke portion 9 bin order for the outer circumferential surface 19 d of the socket wrench19 to escape (in order for the outer circumferential surface 19 d of thesocket wrench 19 to slide on the inclined surface 13 c).

Each of the first yoke portions 9 b, 9 b is provided at a top end sidethereof with a first bearing hole 9 d that penetrates the first yokeportion 9 b from an inner peripheral surface toward an outer peripheralsurface of the first yoke portion 9 b and opens in a radial direction.Then, a first bearing 12 a that holds the cruciform shaft 12 is setinside the first bearing hole 9 d. That is, the cruciform shaft 12 isheld by two first bearings 12 a, 12 a set at the U-shaped top end sideof the first yoke portions 9 b, 9 b.

On the other hand, as for the flange yoke 10, as shown in FIG. 2, in thesame way as the ball yoke 9, the flange yoke 10 is formed as asingle-piece component by casting. The flange yoke 10 has a mountingflange 10 a and a pair of second yoke portions 10 b, 10 b formedintegrally with a top end of the mounting flange 10 a and having abifurcated shape which protrude or extend along an axial direction. Eachof the second yoke portions 10 b, 10 b is provided at a front sidethereof with a second bearing hole 10 c that penetrates the second yokeportion 10 b from an inner peripheral surface toward an outer peripheralsurface of the second yoke portion 10 b and opens in a radial direction.Then, a second bearing 12 b that holds the cruciform shaft 12 is setinside the second bearing hole 10 c. That is, the cruciform shaft 12 isheld by two second bearings 12 b, 12 b set at the U-shaped front side ofthe second yoke portions 10 b, 10 b.

In the same way as the first yoke portions 9 b, 9 b, each of the secondyoke portions 10 b, 10 b is provided at both side surfaces thereof witha second depressed portion 14 that is a second hollow portion (or asecond concave portion). This second depressed portion 14 is formed intoan arc-shaped groove in cross section which is substantially same as anarc shape of an outer peripheral edge of a nut seating surface 15 a(described later) (which is substantially same as the arc shape of theouter circumferential surface 19 d of the socket wrench 19). Further,the second depressed portion 14 is formed along the axial direction froma front end portion of each second yoke portion 10 b up to a positionwhere the second depressed portion 14 faces the nut seating surface 15a. More specifically, as seen in FIG. 2, the second depressed portion 14is formed so as to gradually spread (so as to gradually become wider)from a top end portion 14 a at the front side of the second yoke portion10 b up to a rear end portion 14 b. A depth of the groove is formed soas to gradually become deeper from the top end portion 14 a sideaccording to a reverse taper angle of both side surfaces of the secondyoke portion 10 b, and a middle position in a width direction of thegroove is deepest.

As shown in FIGS. 2 and 3, the flange yoke 10 has an almost rectangularshape, and is provided at four corners thereof with arc-shaped bossportions 15. Further, four bolt insertion holes 16 are formed in themiddle of the respective boss portions 15, then a stud bolt 17(described later) is inserted into this bolt insertion hole 16.

On one side surface of the boss portion 15 which faces the ball yoke 9,the flat nut seating surface 15 a on which a nut 18 (a securing member,described later) is seated is formed. This nut seating surface 15 a isformed so that the second depressed portion 14 faces the nut seatingsurface 15 a.

On the other hand, on a back surface of the flange yoke 10, as shown inFIG. 1, a substantially ring-shaped annular protrusion 10 d that isfitted in a ring groove (not shown) of a mounting plate 11 b (describedlater) formed at the connecting member 11 is provided. By this fittingof the annular protrusion 10 d and the ring groove of the mounting plate11 b, positioning when connecting the flange yoke 10 and the connectingmember 11 is made.

The connecting member 11 has a substantially cylindrical shape as seenin FIG. 2. The connecting member 11 has a cylinder shaft portion 11 athat connects to the output shaft of the transmission, the disk-shapedmounting plate 11 b that is formed integrally with the cylinder shaftportion 11 a at an end of the cylinder shaft portion 11 a opposite tothe flange yoke 10 and the four stud bolts 17 that protrude from a frontend surface, on the flange yoke 10 side, of the mounting plate 11 b.

The stud bolt 17 is previously fixed to four corner positions close toan outer circumferential edge of the mounting plate 11 b. The mountingflange 10 a and the mounting plate 11 b are joined together by screwingthe nut 18 onto the stud bolt 17 from a top side of a shaft portion ofthe stud bolt 17.

The socket wrench 19 as a turning tool (a tightening or fastening tool)to turn and tighten the nut 18 is formed, as shown in FIGS. 5 and 8, bya socket part 19 a at a top side and a relatively long rod handle 19 crotatably connected to a rear end of the socket part 19 a through apivot pin 19 b. The socket part 19 a is cylindrical in shape, and itstop end inside has a hexagonal surface that is fitted onto the nut 18.

Here, regarding the propeller shaft 1, each element or component of thepropeller shaft 1 is previously assembled before the propeller shaft 1is connected to the transmission etc. mounted on the vehicle, thenfinally the propeller shaft 1 is connected to the transmission and thedifferential gear.

[Method of Connecting Propeller Shaft and Transmission]

As a connecting method, as shown in FIG. 4, first, each stud bolt 17 ofthe mounting plate 11 b is inserted into the bolt insertion hole 16 ofthe mounting flange 10 a. Next, the nut 18 is screwed onto each studbolt 17 by hand for temporal fixing until the nut 18 reaches and touchesthe nut seating surface 15 a.

Subsequently, as shown in FIGS. 5 and 6, the socket part 19 a of thesocket wrench 19 is inserted and fitted onto the nut 18 screwed onto thestud bolt 17 from the top side of the stud bolt 17, and the top end ofthe socket part 19 a is fitted onto the nut 18. At this time, the socketpart 19 a is inserted along the stud bolt 17 using the first and seconddepressed portions 13 and 14 of the first and second yoke portions 9 band 10 b. That is, using a relatively large gap or clearance formedbetween inner surfaces of the arc-shaped grooves of the first and seconddepressed portions 13 and 14 and an outer peripheral surface of the studbolt 17, the socket part 19 a can be smoothly inserted.

Next, the socket wrench 19 is turned with the rod handle 19 c rotated upto about 90° through the pivot pin 19 b, then the nut 18 is tightenedwith a required or specified torque.

After tightening, the socket wrench 19 is pulled out in a direction ofan arrow shown in FIGS. 7 and 8, namely, pulled out linearly along anaxial direction of the stud bolt 17, and the socket part 19 a is removedor separated from the nut 18. That is, the rod handle 19 c is returnedto the same axis as the socket part 19 a through the pivot pin 19 b andis pulled up linearly. At this time, since the socket part 19 a and therod handle 19 c can be pulled out along the inner surfaces of thearc-shaped grooves of the first and second depressed portions 13 and 14,the socket wrench 19 can be smoothly pulled out or detached withoutinterfering with any side surface of the first and second yoke portions9 b and 10 b.

Especially when the socket wrench 19 can not easily be detached from thenut 18 due to the fact that the inside hexagonal surface of the socketpart 19 a is jammed onto or engaged with a hexagonal surface of the nut18 after tightening the nut 18 with the specified torque, this structureis effective in the event that the whole socket wrench 19 is pulled upin a vertically upward direction while being pulled out along a longlength of the axial direction of the stud bolt 17.

Afterwards, likewise, the socket wrench 19 can easily be inserted andfitted onto and detached from the other three nuts 18. The methoddescribed above facilitates a connecting work (or a tightening work) ofthe mounting flange 10 a on the propeller shaft 1 side and the mountingplate 11 b on the transmission side. Efficiency and workability of theconnecting work can be therefore increased.

As for the connection between the propeller shaft 1 and the differentialgear, since it is done by the same connecting method, its explanationwill be omitted here.

As explained above, according to the present embodiment, since the firstand second depressed portions 13 and 14 formed on the both side surfacesof the first and second yoke portions 9 b and 10 b can be used as anescape groove (or a sliding groove) when inserting and detaching thesocket wrench 19, it is possible to suppress the interference of thesocket wrench 19 with the both side surfaces of the first and secondyoke portions 9 b and 10 b, thereby allowing the smooth inserting anddetaching work of the socket part 19 a.

Further, since the first and second depressed portions 13 and 14 havethe arc-shaped groove which is substantially same as the arc shape ofthe outer circumferential surface 19 d of the socket part 19 a, wheninserting and detaching the socket part 19 a of the socket wrench 19,the first and second depressed portions 13 and 14 serve as a guidingportion for the socket wrench 19. Thus the smooth inserting anddetaching work can be achieved.

Furthermore, since the first depressed portion 13 has the inclinedsurface 13 c having the reverse tapered shape from a front edge of thecylinder portion 9 a toward the middle position in the axial directionon the outer circumferential surface of the cylinder portion 9 a, whendetaching the socket part 19 a of the socket wrench 19 from the nut 18,the inclined surface 13 c serves as a guiding portion that guides thesocket wrench 19 in a pulling-out direction. Thus the smooth detachingwork can be achieved.

Moreover, since the reverse tapered-shaped inclined surface 13 c locatedat the rear edge of the rear end portion 13 b of the first depressedportion 13 rises toward the outer circumferential surface of thecylinder portion 9 a, the interference of the socket wrench 19 with thecylinder portion 9 a when pulling out the socket wrench 19 is avoided.It is therefore possible to decrease a stress concentration that appliesto the cylinder portion 9 a by the socket wrench 19.

In addition, since the second depressed portion 14 is formed along theaxial direction from the front end portion of each second yoke portion10 b up to the position where the second depressed portion 14 faces thenut seating surface 15 a, a long space on the inner surface side of thesecond depressed portion 14 can be secured in the axial direction. Thus,when inserting the socket wrench 19 along the stud bolt 17, interferenceof the socket wrench 19 with the both side surfaces of the seconddepressed portion 14 can be further suppressed.

Second Embodiment

FIG. 9 shows a second embodiment. In the second embodiment, a pitchdistance between the bolt insertion holes 16 formed at the mountingflange 10 a is changed. That is, a central angle formed by two positionsof the adjoining two bolt insertion holes 16 and 16 that sandwich thesecond yoke portion 10 b (i.e. a central angle formed by two positionsof the adjoining two bolt insertion holes 16 and 16 that are placed onopposite sides of the second yoke portion 10 b) is set to 100°, and acentral angle formed by two positions of the adjoining two boltinsertion holes 16 and 16 that sandwich no second yoke portion 10 b isset to 80°.

Thus, according to the present embodiment, the present invention can beapplied also to the mounting flange 10 a where the bolt insertion holes16 are not arranged uniformly.

Since the other structure of the second embodiment is the same as thatof the first embodiment, the same effects as the first embodiment can beobtained.

The position and distance (or interval) of the bolt insertion holes 16could be changed to an arbitrary numerical value. In some cases, eachposition of the boss portion 15 formed at the mounting flange 10 a ofthe second yoke 10 (the flange yoke 10), i.e. each position of the boltinsertion hole 16, is separate from each of the both side surfaces ofthe second yoke portion 10 b. In this case, since the interference ofthe socket part 19 a of the socket wrench 19 with the both side surfacescan be avoided, there is no need to form the second depressed portion 14at the second yoke 10.

Further, although the stud bolt 17 is used when connecting the mountingflange 10 a and the mounting plate 11 b, a commonly-used bolt could beused.

The present invention is not limited to the embodiments described above,and the above embodiments can be modified.

From the foregoing, the present invention includes the followingstructure of the propeller shaft and the yoke structure of the universaljoint used for the propeller shaft, and has the following effects.

(a) In the propeller shaft of the present invention, the second yoke hasa pair of second yoke portions having a bifurcated shape that extendsfrom the mounting flange toward the first yoke in the axial direction, asecuring member seating surface corresponding to a size of the securingmember is formed around the bolt insertion hole of the mounting flange,and a second concave portion is provided at each second yoke portion sothat the securing member seating surface is visible from a front endside of the second yoke portion.

According to the present invention, since the second concave portion ofthe arc-shaped groove is formed at the second yoke portion, wheninserting and detaching the fastening tool, the fastening tool does notinterfere with the second yoke portion, then the efficiency andworkability of the connecting work can be increased.

(b) In the propeller shaft, the mounting flange is provided with fourbolt insertion holes at a predetermined pitch distance, and the secondconcave portion is formed at both side surfaces of the second yokeportion, and is shaped into an arc-shaped groove in cross section thatextends in a longitudinal direction of the second yoke portion.

According to the present invention, even though the second concaveportion is formed at both side surfaces of the second yoke portion, whenthe cruciform shaft is set into the bearing hole, this structure doesnot interfere with the cruciform shaft setting work.

(c) In the propeller shaft, the bolt insertion hole is arranged in aposition corresponding to a position of the second concave portionformed at the both side surfaces of the second yoke portion, and thesecond concave portion is formed so that a substantially middle in awidth direction of the second concave portion is deepest.

According to the present invention, a strength in a side surfacedirection of the second yoke portion can be kept uniform.

(d) In the propeller shaft, the four bolt insertion holes are arrangedso as to form two predetermined central angles, and a first two of thefour bolt insertion holes are arranged in positions that sandwich one ofthe pair of second yoke portions at a predetermined distance, and asecond two of the four bolt insertion holes are arranged in positionsthat sandwich the other of the pair of second yoke portions with thesecond two bolt insertion holes spaced a distance that is smaller thanthe predetermined distance apart from the first two bolt insertionholes, and the second concave portion is formed in a thickness directionof the side surface that is continuously formed on opposing surfaces ofthe second yoke portion.

According to the present invention, this structure can be applied alsoto the mounting flange where the bolt insertion holes are not arrangeduniformly.

(e) In the propeller shaft, the outer circumferential surface of thefastening tool is cylindrical in shape, and

the first concave portion is formed into a shape corresponding to theouter circumferential surface of the fastening tool.

According to the present invention, since the first concave portion isformed into the same shape as an outside shape of the fastening tool,even if the fastening tool touches the first concave portion wheninserting and detaching the fastening tool, the fastening tool is guidedby the first concave portion, then the fastening tool can be insertedand detached smoothly.

(f) In the propeller shaft, the fixing portion is formed by a cylinderportion, and the first concave portion is formed from a front end sideof the first yoke portion to a substantially middle position in theaxial direction on an outer circumferential surface of the cylinderportion.

According to the present invention, since the first concave portion isformed from the front end side of the first yoke portion to thesubstantially middle position in the axial direction on the outercircumferential surface of the cylinder portion, an area or a space ofthe first concave portion can be widely secured in the axial direction.It is therefore possible to suppress the interference of the fasteningtool with the first yoke portion when detaching the fastening tool.

(g) In the propeller shaft, the first concave portion is formed so thata depth of the first concave portion gradually becomes deeper up to apredetermined depth from a front end side of the first yoke portion, anda rear end portion of the first concave portion is shaped into aninclined surface having a reverse tapered shape.

According to the present invention, since the rear end portion of thefirst concave portion is shaped into the inclined surface, theinterference of the socket wrench is avoided when detaching the socketwrench, then a stress concentration applying to the rear end portion ofthe first concave portion by the socket wrench can be decreased.

(h) In the propeller shaft, the inclined surface is a guiding portionwhen detaching the fastening tool from the nut.

According to the present invention, since the rear end portion of thefirst concave portion is shaped into the inclined surface, even if thefastening tool touches the first concave portion when detaching thefastening tool, the fastening tool is guided by the first concaveportion, then the fastening tool can be detached smoothly.

(i) In the propeller shaft, the first concave portion is formed from afront end portion of the first yoke portion to a substantially middleposition in the axial direction on an outer circumferential surface ofthe cylinder portion.

According to the present invention, since the first concave portion isformed from the front end portion of the first yoke portion to thesubstantially middle position in the axial direction on the outercircumferential surface of the cylinder portion, an area or a space ofthe first concave portion can be widely secured in the axial direction.It is therefore possible to suppress the interference of the fasteningtool with the first yoke portion when detaching the fastening tool.

(j) In the propeller shaft, the flange yoke has a pair of second yokeportions having a bifurcated shape that extends from the flange towardthe ball yoke in the axial direction, a nut seating surface is formedaround the bolt insertion hole of the flange, and a second concaveportion is provided at each second yoke portion so that the nut seatingsurface is visible from a front end side of the second yoke portion.(k) In the propeller shaft, the flange is provided with four boltinsertion holes at a predetermined pitch distance, and the secondconcave portion is formed by a concave groove that extends in the axialdirection on both side surfaces of the second yoke portion.(l) In the yoke structure of the universal joint, the fixing portion isformed by a cylinder portion, and the concave portion is formed from afront end side of the yoke portion to a substantially middle position inthe axial direction on an outer circumferential surface of the cylinderportion.

According to the present invention, since the first concave portion isformed from the front end portion of the first yoke portion to thesubstantially middle position in the axial direction on the outercircumferential surface of the cylinder portion, an area or a space ofthe first concave portion can be widely secured in the axial direction.It is therefore possible to suppress the interference of the fasteningtool with the first yoke portion when detaching the fastening tool.

(m) In the yoke structure of the universal joint, the concave portion isformed so that a depth of the concave portion gradually becomes deeperup to a predetermined depth from a front end side of the yoke portion,and a rear end portion of the concave portion is shaped into an inclinedsurface having a reverse tapered shape.

According to the present invention, since the rear end portion of thefirst concave portion is shaped into the inclined surface, theinterference of the socket wrench is avoided when detaching the socketwrench, then a stress concentration applying to the rear end portion ofthe first concave portion by the socket wrench can be decreased.

(n) In the yoke structure of the universal joint, the inclined surfaceis a guiding portion when detaching the fastening tool from the nut.

According to the present invention, since the rear end portion of thefirst concave portion is shaped into the inclined surface, even if thefastening tool touches the first concave portion when detaching thefastening tool, the fastening tool is guided by the first concaveportion, then the fastening tool can be detached smoothly.

The entire contents of Japanese Patent Application No. 2013-112667 filedon May 29, 2013 are incorporated herein by reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

What is claimed is:
 1. A propeller shaft comprising: a shaft part; afirst yoke having a fixing portion, a connecting portion that is formedintegrally with the fixing portion, a first yoke portion and a firstconcave portion, wherein the first yoke is connected, through theconnecting portion, to one end of the shaft part in a direction of arotation axis of the shaft part, the first yoke portion is provided atthe fixing portion such that the first yoke portion protrudes from thefixing portion in a direction away from the one end of the shaft partalong, the direction of the rotation axis of the shaft part, the firstconcave portion is provided at an end portion of the fixing portion soas to accommodate thereon an outer circumferential surface of afastening tool that fastens a securing member, separate from theconnecting portion in the direction of the rotation axis of the shaftpart, and has a concave shape that opens toward a radial direction outerside of the rotation axis of the shaft part, and the connecting portionis provided apart from the first concave portion in the direction of therotation axis of the shaft part, and an outside diameter of theconnecting portion is greater than an outside diameter of the shaft partin a radial direction of the rotation axis of the shaft part; a secondyoke having a flange and a second yoke portion, wherein the flange isprovided so as to face the first yoke portion in the direction of therotation axis of the shaft part, the flange also has a bolt insertionhole into which the securing member is inserted, and is connected to asecond shaft part of a vehicle side by the securing member, and thesecond yoke portion is provided at the flange such that the second yokeportion protrudes from the flange toward the one end of the shaft part,in the direction of the rotation axis of a shaft part; and a cruciformshaft coupling the first yoke portion with the second yoke portion. 2.The propeller shaft as claimed in claim 1, wherein: the bolt insertionhole of the flange is provided at a position opposing to the end portionformed at the fixing portion in the direction of the rotation axis ofthe shaft part.